是否可以使用块定义一个Ruby单例方法？ [英] Is it possible to define a Ruby singleton method using a block?

问题描述

所以，我想为一个对象定义一个singleton方法，但我想使用一个闭包。

例如，

  def define_say（obj，msg）
 def obj.say 
 puts msg 
 end 
 end 
 
o = Object.new 
 define_say o，hello world！ 
 o.say 
  

这不起作用，因为通过def定义了一个单例方法，不是一个闭包，所以我得到一个异常，msg是一个未定义的变量或方法。

我想做的就像使用define_method方法在Module类中，但是据我所知，这只能用于在类上定义一个方法...但我想要一个Singleton方法...

所以，我想写这样的东西：

  def define_say（obj，msg）
 obj.define_singleton_method（：say）{
 puts msg 
} 
 end 
  

有没有人知道我可以如何实现这一点，而无需创建一个方法来存储一个Proc，然后在单一方法中使用Proc？ （基本上，我想要一个干净，非黑客的方式这样做）

解决方案

这里有一个答案，寻找

  def define_say（obj，msg）
＃获取obj的singleton类的句柄
 metaclass = class<< obj;自; end 
 
＃添加使用define_method而不是def x.say的方法，所以我们可以使用闭包
 metaclass.send：define_method，：say do 
 puts msg 
 end 
 end 
  

使用（从IRB粘贴）

 >> s =my string
 => my string
>> define_say（s，I am S）
 => ＃< Proc：0xb6ed55b0 @（irb）：11> 
>> s.say 
我是S 
 => nil 
  

有关更多信息（和一个小图书馆， >

http://viewsourcecode.org/why/ hacking / viewingMetaclassesClearly.html

另外，如果你是一个红宝石程序员，而你还没有读过，现在就去吧！

So, I want to define a singleton method for an object, but I want to do it using a closure.

For example,

def define_say(obj, msg)
  def obj.say
    puts msg
  end
end

o = Object.new
define_say o, "hello world!"
o.say

This doesn't work because defining a singleton method via "def" is not a closure, so I get an exception that "msg" is an undefined variable or method.

What I would like to do is something like using the "define_method" method in the Module class, but as far as I can tell, this can only be used to define a method on a class... but I want a Singleton Method...

So, I would love to write it something like this:

def define_say(obj, msg)
  obj.define_singleton_method(:say) {
    puts msg
  }
end

Does anyone know how I can achieve this without having to create a method to store a Proc and then use the Proc within a singleton method? (basically, I want a clean, non-hacky way of doing this)

解决方案

Here's an answer which does what you're looking for

def define_say(obj, msg)
  # Get a handle to the singleton class of obj
  metaclass = class << obj; self; end 

  # add the method using define_method instead of def x.say so we can use a closure
  metaclass.send :define_method, :say do
    puts msg
  end
end

Usage (paste from IRB)

>> s = "my string"
=> "my string"
>> define_say(s, "I am S")
=> #<Proc:0xb6ed55b0@(irb):11>
>> s.say
I am S
=> nil

For more info (and a little library which makes it less messy) read this:

http://viewsourcecode.org/why/hacking/seeingMetaclassesClearly.html

As an aside, If you're a ruby programmer, and you HAVEN'T read that, go do it now~!

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